The out-of-control creatures are far more terrifying than the invading creatures by countless times!
These creatures do not belong to any one world, and no one knows how they are born. It is only known from some clues that the emergence of out-of-control creatures is extremely complex, belonging to post-natal creation, and eventually evolving into beings that can destroy all worlds.
For example, the Demon Race, such out-of-control creatures, are naturally capable of invading other worlds, and most of them have the talent to weaken the suppression from other worlds.
This gives them an advantage far exceeding any other creatures when invading other worlds, if not making them feel at home.
Moreover, due to the reason that such out-of-control creatures do not belong to any world and ecological chain, wherever they go, they will gradually lead that world to collapse.
